There is a growing need for alternative sources of alkali metals, such as, but not limited to, potassium. Potassium chloride (traditional potassium fertilizing agent) is produced in a limited number of geographical locations remote from the southern hemisphere, where the transportation costs contribute to the market price significantly, making local manufacturing of potassium fertilizer increasingly attractive. As human population grows, agriculture also must grow and evolve with it, in particular, in available regions in the southern hemisphere. Among others, modern agriculture development in those regions requires growing crops on soils that are often fully depleted of macronutrients, structural elements, e.g. silicon in a form available for plants (monosilicic acid) or calcium, and structure-developing minerals, such as clay minerals (phylosilicates). In other words, these soils are not optimal for growing crops due to the lack of proper structure and essential elements resources. From the perspective of soil fertilization, traditional fertilizing agents, such as potassium nitrate and potassium chloride, are not optimal due to their excessive leaching, the lack of retention of their corresponding ions, and their inability to provide a proper structure to the soil. Potassium and other nutrition elements introduced into the soil in the form of these highly soluble salts are thus wasted, having potential negative effects on the environment, e.g., chloride contamination. Therefore, new potassium sources and a better means of nutrient delivery are needed to allow high agricultural productivity and expansion in the available regions of the southern hemisphere. Ideally, these sources can simultaneously provide essential elements, such as calcium and plant-available silicon, and promote formation of structural minerals.
Rock-forming minerals, such as potassium feldspars (KAlSi3O8), may therefore be considered as earth-abundant alternatives to traditional sources based on their relatively high content of K2O (more than 15 wt % of K2O in pure KAlSi3O8). Numerous research efforts dedicated to the extraction of potassium ion (K+) from rock-forming minerals have been conducted in the last decades. Among such proposals are methods for complete disintegration of potassium-bearing silicates and aluminosilicates aimed at extracting K+ in the form of a highly soluble salt, such as, but not limited to KCl. These extraction methods are typically based on the precipitation of a water-soluble potassium salt from an aqueous solution obtained after disintegration of the raw minerals. The methods of disintegration, in turn, typically employ relatively high temperatures (>1000° C.), or/and aggressive acid-basic treatments, inevitably creating large volumes of liquid and/or solid wastes involving sophisticated and expensive separation techniques. (“Processing for decomposing potassium feldspar by adopting low-temperature semidry method for comprehensive utilization,” CN 103172074 A; Hao Zhang, et al. (2012). The Extraction of Potassium from Feldspar by Molten Salt Leaching Method with Composite Additives. Advanced Materials Research, 524-527, 1136; and Pedro Lucas Gervasio Ladiera Potash product and method Patent Application WO 2013061092 A1. The teachings of all of which are incorporated herein by reference in their entirety.)
Attempts to use unaltered stone-meals (crushed rocks) as an alternative source of potassium for fertilizer and a source of plant-available silicon have also been made. (Anne Kjersti Bakken, Harvard Gautneb, Kristen Myhr (1997) Plant available potassium in rocks and mine tailings with biotite, nepheline and K-feldspar as K-bearing minerals. Acta Agriculturae Scandinavica, Section B—Soil & Plant Science. Vol. 47; and Y. Tokunaga, Potassium silicate (1991). A slow-release potassium fertilizer. Fertilizer Research. 30, 55-59. The teachings of all of which are incorporated herein by reference in their entirety.) However, natural chemical weathering of those crushed stone is an extremely slow process, and the benefits such as nutrients release and phylosilicate formation from crushed primary minerals appear only on a timescale that far exceed—several years, potentially decades—the timescale of growth and harvesting of crops of modern agriculture.
Therefore, a need exists to produce a source of potassium ion that releases the nutrient at a moderate rate, lower than the infinite dissolution rate of a traditional salts, but faster than the rate generally exhibited by naturally-occurring minerals. Ideally, this source be produced from the earth abundant K-bearing silicate rocks, can provide structural components (such as silicon in the form of monosilicic acid and/or calcium), and can promote the formation of clay minerals (phylosilicates). Also, a need exists for a method to produce source of such materials that minimizes the above-mentioned problems.